Adding convert_from_taggroup() function

• Adding __file__ variable is now always given in dm-script containing the current dm-script file
  path
• Adding ingore markers @execdmscript.ignore.start and @execdmscript.ignore.end to allow code
  that is only executed in direct dm-script calls
• Adding convert_from_taggroup() function that converts DigitalMicrograph.Py_TagGroup to
  dicts, lists which is the opposite function to convert_to_taggroup()
• Adding helper documentation in README
• Adding examples for get_dm_type() and get_python_type()
• Adding examples for escape_dm_variable() and escape_dm_string()
• Adding examples for convert_from_taggroup() and convert_to_taggroup()